Keep it simple: There are a million different to-do apps, what makes one stand out? This week on Track Changes Paul and Rich chat with Doist founder Amir Salihefendic. He tells us about how he grew Todoist from a side project he would work on in his dorm room to an app that now reaches 20 million people. He also tells us about his struggle with venture capitalists and about the importance of persistence and simplicity.